This presentation is about methods of gene transfer in bacteria.

1. Gene Transfer Mechanisms
in Bacteria
Prsented by:
Sanjay Kr Vishwakarma

2. Gene transfer mechanisms in bacteria
• Conjugation: orderly, deliberate transfer of DNA from one cell
to another; programmed by specialized genes and organelles.
• Transformation: uptake of environmental DNA into a cell
• Transduction: transfer of DNA from one cell to another
mediated by a virus

4. Properties of gene transfer in bacteria
• All are unidirectional (donor–recipient)
• Recombination requires two steps:
1. Transfer of DNA into the recipient cell, forming a merozygote (various gene
transfer mechanisms)
2. Crossing over that replaces a portion of the recipient genome (endogenote)
with the homologous portion of the donor genome (exogenote)
• Transfer is always partial

5. Conjugation

6. • Direct transfer via connection tube, one-way traffic from donor cells
to recipient cells.
• It is not a reciprocal exchange of genetic information.
• F+ cells donor cells containing F factor
• F− cells recipient cells lacking F factor
• Sex Pilus – connection tube

7. Conjugation in E. coli is based on the F (fertility)
plasmid

8. Transfer of integrated F includes donor
chromosome
Unidirectional
transfer
Recombination
Partial transfer

9. DNA transfer during conjugation is time-dependent
Transfer of an entire E. coli donor genome requires about 1 hour (F
sequence is last to transfer)
The chromosome as a time function:
• Mix donor Hfr and recipient F- cells
• Interrupt transfer of DNA at various times
• Plate out cells to determine which genes were transferred within each
timeframe

10. Hfr azir tonr lac+ gal+ strs X F- azis tons lac- gal- strr

11. Transformation
DNA in the environment of a cell is taken into the recipient cell
forming a merozygote; then recombination occurs
• Competent cells: cells that take up DNA
• Transformants: cells that receive genetic material
• Cotransformed: cells that are transformed by two or more genes

13. Transduction
Transduction: Transfer of DNA from one cell to another mediated by
a virus; followed by recombination to integrate the DNA into the
recipient cell.
• General transduction: any genes can be transferred
• Specialized transduction: only a few genes can be transferred

15. Bacteriophages have two alternative life cycles:
lytic and lysogenic

16. Multiple Choice Question

17. 1. The Hfr chromosome is transferred to the F— cell in a _____________ fashion.
a) circular
b) coiled
c) dimer
d) linear

18. 1. The Hfr chromosome is transferred to the F— cell in a _____________ fashion.
a) circular
b) coiled
c) dimer
d) linear
Answer: d

19. 2. Which of the following is true for an Hfr X F— cross?
a) frequency of recombination high, transfer of F factor low
b) frequency of recombination high, transfer of F factor high
c) frequency of recombination low, transfer of F factor high
d) frequency of recombination low, transfer of F factor low
Answer: a

20. 2. Which of the following is true for an Hfr X F— cross?
a) frequency of recombination high, transfer of F factor low
b) frequency of recombination high, transfer of F factor high
c) frequency of recombination low, transfer of F factor high
d) frequency of recombination low, transfer of F factor low
Answer: a

21. 3. Introduction of DNA molecules into the recipient organism is termed as ____________
a) transformation
b) translation
c) transduction
d) transcription
Answer: a

22. 3. Introduction of DNA molecules into the recipient organism is termed as ____________
a) transformation
b) translation
c) transduction
d) transcription

23. 4. Which of the following role is performed by a bacteriophage in transduction?
a) vector
b) donor
c) recipient
d) episome
Answer: a

24. 4. Which of the following role is performed by a bacteriophage in transduction?
a) vector
b) donor
c) recipient
d) episome

25. Answer key:
1- d
2-a
3-a
4-a

26. Thank You